1. Field of the Invention
The present invention relates to a housing and method of sealing same for an electrical component and in particular to such a housing and method which make use of the capillary action of channels in the housing to draw sealing compound to close and seal all housing gaps.
2. Description of the Prior Art
Many electrical components such as, for example, relays are contained in a housing consisting of a base and a cap with the base having a number of openings therein for receiving various contacts. In order to insure a hermetic seal of the component, all gaps and contact openings in the housing are sealed with a sealing compound, such as a suitable resin. It is known to introduce the sealing compound via a dispensing point in the base or through wider filling channels so that the sealing compound is conveyed to the housing joints which are to be sealed by means of the capillary action of the channel system. Such a structure and method of sealing electronic components in a housing are known, for example, for German utility patent No. 7,821,508 and United Kingdom Pat. No. 2009532 A.
In conventional structures and methods, all of the points which are to be sealed are supplied with sealing compound from a common reservoir or are connected to one another at least via the channel system or a network of channels. In known structures this network of channels exhibits additional cross connections in order to achieve a good distribution of the sealing compound. This method and apparatus for sealing a housing is adequate if all of the capillary gaps and channels which are to be sealed from a single dispensing point are identical, however, the supply of all of the capillary network from a single dispensing point does not provide an adequate seal if, because of specific construction necessities and/or tolerances, different sized joints are to be sealed in a single component. A similar disadvantage results if the flow paths between the dispensing point and the joints which are to be sealed are of vastly different lengths or if the viscosity of the sealing compound is not optimally adapted to the various capillaries. Additionally, fluctuations in the viscosity of the sealing compound which may be caused, for example, by changes in the temperature, have a similarly unfavorable influence on the overall seal which is achieved. The above factors can cause an ineffective seal for the reason that the capillary action of the joints or gaps is greatly dependent upon the geometric shapes thereof, that is, upon the length of the joints, and is also dependent upon the viscosity of the resin. Differences in either of these characteristics can result in widely differing suction or capillary forces within different capillary networks. This in turn results in the fact that the casting compound is drawn in greater volume into narrow gaps and, because of the common sealing compound supply via the channel network in conventional structures, the sealing compound may even be drawn out of the wider gaps which have initially been closed and filled with sealing compound as a result of an initial uniform distribution.
The above problem cannot always be solved by simply supplying additional sealing compound because the excess sealing compound will not necessarily remain in the gaps with a low capillary action but will more likely be drawn into the gaps of high capillary action which are already filled to excess. When the volume of sealing compound in such gaps exceeds the volume of the gap such as, for example, as a result of the additionally occurring gravitational force, the sealing compound may flow into the interior of the housing which must be avoided at all costs.